Dual clutch transmissions known from practical experience, on which high performance demands are placed, are provided with an appropriately efficient cooling concept. In such transmissions, the cooling, which is necessary depending on the operating condition, of wet-running multi-disk clutches of a dual clutch system as well as of further transmission components, such as an all-wheel clutch, is ensured with the aid of an actuation of a cooling valve of an electro-hydraulic transmission control system according to demand. Such a cooling valve is a pressure control valve in this case when cooling oil is applied via the cooling valve essentially only to the multi-disk clutches of the dual clutch system. As a result, the entire actuating range is largely usable for the regulation, which positively affects the achievable accuracy.
If, in addition to the need for clutch cooling, there are demands for variable gear set cooling as well as cooling which, overall, is utilized according to demand and is optimal in terms of energy consumption, the cooling valve is a pilot-controllable distributor valve, as is known. Such cooling valves, which are also referred to as cooling oil distributor valves, are pilot controlled, for example, with the aid of an electromagnetic pressure regulator or an electromagnetic pilot stage, in the area of which a pilot pressure is set as a function of an actuating current and an applied supply pressure. The pilot pressure, in turn, is applied in order to actuate the cooling valve.
An electro-hydraulic transmission control system comprising such a cooling oil distributor valve is known, for example, from DE 10 2014 207 798 A1.
In principle, the stationary relationship between the input parameter, i.e., the actuating current of the electromagnetic pilot stage, and the associated output parameter, i.e., in this case, the particular distribution factors of the hydraulic fluid applied at the cooling valve in the direction of dual clutch system as well as further areas of the dual clutch transmission, are graphically representable as a so-called cooling oil characteristic curve, wherein the term “distribution factor” is understood to mean the percentage distribution, which is adjustable in the area of the cooling valve with the aid of the pilot control, of the available cooling oil between the component or areas of the dual clutch transmission to be cooled.
In order to be able to operate a dual clutch transmission with the highest possible efficiency, a variable displacement pump is provided for the hydraulic supply, with the aid of which not only the cooling oil valve, but also further hydraulic consumers of the dual clutch transmission, such as clutch actuators, shift actuators of the dual clutch transmission, and the like, are supplied with hydraulic fluid. The volumetric output flow of such a variable displacement pump, which is not required for the supply of primary hydraulic consumers of the dual clutch transmission, is routed in the direction of a cooling and lubricating circuit of a dual clutch transmission and is distributed to the particular transmission components to be cooled and to be lubricated, depending on the thermal demands.
In addition, a so-called system pressure valve is provided for setting a system pressure required for the operation of the consumers. The system pressure valve is also actuated with the aid of an electromagnetic pilot stage.
FIG. 2 shows profiles of various distribution factors of a cooling valve with respect to an actuating current i_EDS of an electro-hydraulic pressure regulator of an electro-hydraulic transmission control system associated with the cooling valve. In the area of the electro-hydraulic pressure regulator, in turn, a pilot pressure is set as a function of the particular actuating current i_EDS. The pilot pressure is applicable at the cooling valve and, depending on which, in turn, a valve slide of the cooling valve is displaceable between a first defined end position and a second defined end position in order to be able to route the hydraulic fluid volume, which is applied at the cooling valve, to the desired extent in the direction of the areas of the transmission which is, for example, a dual clutch transmission.
In this case, the profile v_sa indicates the particular portion of the hydraulic fluid flow applied at the cooling valve, which, at the particular set actuating current value i_EDS, is routed in the direction of a suction loading of a hydraulic pump of the transmission, while the profile v_kk indicates the portion of the hydraulic fluid flow applied at the cooling valve, which, at the currently set current value i_EDS, is routed starting from the cooling valve in the direction of a dual clutch system of the transmission. The further profile v_rs, in turn, indicates the particular portion of the hydraulic fluid flow applied at the cooling valve with respect to the actuating current i_EDS of the electro-hydraulic pressure regulator, which is applied to a particular gear set of the transmission for cooling purposes.
The schematic representation, shown in FIG. 2, of the distribution of the hydraulic fluid volume applied at the cooling valve in the direction of the suction loading of the hydraulic pump, the clutch cooling, and the gear set cooling with respect to the actuating current i_EDS of the electro-hydraulic pressure regulator shows a stationary relationship between the actuating current i_EDS and the particular associated distribution factor of the cooling valve for the available hydraulic fluid volume. In this case, the distribution factors v_sa, v_kk and v_rs correspond to the percentage distribution of the available hydraulic fluid volume between the components or areas of the transmission to which the hydraulic fluid volume is to be applied.
In order to be able to actuate the cooling valve with the demanded accuracy, the stationary dependence is determined on a special component test bench before the transmission is delivered. Therefore, specimen-specific tolerances in the area of the pilot stage or the electro-hydraulic pressure regulator as well as geometric and mechanical tolerances of the electro-hydraulic transmission control system are represented. The data determined on the component test bench are stored in a so-called bin file and are flashed or uploaded into a control unit in the overall vehicle in a manner which is appropriate for the installed transmission.
In a first target value range i_EDSA of the actuating current i_EDS between a current value equal to zero and a first current value i_EDS1, the distribution factor v_rs is essentially equal to zero, while the distribution factors v_sa and v_kk are greater than zero and each have a constant profile. The distribution factor v_kk is less than the distribution factor v_sa within the first target value range i_EDSA. Starting at the current value i_EDS1, the distribution factor v_kk continuously increases, within a second target value range i_EDSB of the actuating current i_EDS, with a high gradient in the direction toward 100%, while the distribution factor v_sa decreases, within a second target value range i_EDSB of the actuating current i_EDS, to the same extent in the direction toward zero, and the distribution factor v_rs is essentially equal to zero within the second target value range i_EDSB. In this case, the distribution factor v_kk is equal to 1, i.e., 100%, starting at a second current value i_EDS2. As the current value i_EDS of the electro-hydraulic pressure regulator increases further within a third target value range i_EDSC of the actuating current i_EDS between the second current value i_EDS2 and a third current value i_EDS3, the hydraulic fluid volume applied at the cooling valve is essentially conducted completely in the direction of the dual clutch system.
Starting at a third current value i_EDS3, the portion of the hydraulic fluid volume applied at the cooling valve, which is routed in the direction of the dual clutch system, constantly decreases within a fourth target value range i_EDSD of the actuating current i_EDS, while the distribution factor v_rs of the cooling valve constantly increases. At a fourth current value i_EDS4, the fourth target value range i_EDSD ends and the distribution factor v_rs is equal to 1, while the distribution factor v_kk has the value zero. As the actuating current i_EDS increases further, the profile of the distribution factor v_rs has a constant value equal to one, starting at the fourth current value i_EDS4, within a fifth target value range i_EDSE of the actuating current i_EDS adjoining the fourth target value range i_EDSD. In this case, the fourth current value i_EDS4 corresponds to the base point of the cooling oil distribution in the direction of the clutch cooling or the supply of the dual clutch system with hydraulic fluid volumes.
The current values i_EDS1 to i_EDS4 are so-called support points of the characteristic curves of the distribution factors v_sa, v_kk, and v_rs, at each current value i_EDS1, i_EDS2, i_EDS3, i_EDS4 a significant change of the gradient of the profile of the distribution factor v_sa, of the distribution factor v_kk, and of the distribution factor v_rs takes place.
Therefore, the actuating range of the cooling valve or of the cooling oil distribution valve in the example shown in FIG. 2 is subdivided into five target value ranges i_EDSA to i_EDSE of the actuating current i_EDS, i.e., five operating ranges of the cooling valve. The cooling oil which is available in a particular case is simultaneously conducted or distributed via the cooling valve, at most, in the direction of two hydraulic consumers.
In the first operating range of the actuating range of the cooling valve, the profiles v_kk, v_sa, and v_rs encompass characteristic curve ranges v_kk1, v_sa1, and v_rs1, respectively, i.e., a so-called plateau in each case, wherein the plateau v_kk1 of the profile v_kk lies at a defined level a of the distribution factor v_kk between zero and 100%. The plateaus v_kk1 and v_sa1 of the profiles v_kk and v_sa are followed by characteristic curve ranges extending across the second target value range i_EDSB, i.e., first transition ranges v_kk2 and v_sa2 of the profiles v_kk and v_sa, respectively, the gradients of which are correspondingly high. Within the third target value range i_EDSC, i.e., the third operating range of the actuating range of the cooling valve, the profiles v_kk, v_sa, and v_rs encompass characteristic curve ranges or plateaus v_kk3, v_sa3, and v_rs3, respectively, having a gradient equal to zero.
Within the fourth target value range i_EDSD, i.e., within the fourth operating range of the actuating range of the cooling valve, the profiles v_kk and v_rs, in turn, encompass characteristic curve ranges or transition ranges v_kk4 and v_rs4, respectively, having high gradients, while the profiles v_kk and v_rs within the fifth operating range of the actuating range of the cooling valve following the fourth operating range encompass characteristic curve ranges v_kk5 and v_rs5, respectively, i.e., plateaus having a slope equal to zero.
Both the second as well as the fourth operating ranges i_EDSB and i_EDSD, respectively, of the actuating range of the cooling valve are relevant for a precise actuation of the cooling valve, which is why they define the respective sections v_kk2 and v_kk4 of the characteristic curve v_kk, i.e., of the cooling characteristic curve, to be considered in greater detail, and only a relatively narrow part of the tolerance-affected actuating range is usable. This, in turn, has a significant influence on the achievable accuracy, because small inaccuracies with respect to the energization of the electro-hydraulic pressure regulator generate high inaccuracies with respect to the cooling valve to be actuated with the aid of the electro-hydraulic pressure regulator, and, therefore, with respect to the particular distribution factors v_kk, v_sa, and v_rs of the cooling valve representing the output parameter.
This is due to the fact, in the case under consideration, that the accuracy of the distribution factor v_kk, v_sa, or v_rs to be adjusted depends on the achievable accuracy of the utilized hydraulic pilot stage and the tolerances of the valve switching actuated therewith. The output parameter of the pilot stage, which is a pilot pressure, is strongly dependent on the hysteresis of its electromagnetic circuit in the case of conventional components. Finally, this pilot pressure is converted into a displacement signal of the actuated cooling valve with the aid of the valve switching. With respect to this pressure-displacement conversion, however, particle contamination in the utilized oil medium, as well as static- and kinetic-friction effects between the valve slide and its bore, which are influenced by shape and position tolerances, production inclusions on the particular surfaces, and the like, can cause undesirable errors in the conversion of the displacement signal. These undesirable errors are significant, in particular, in the case of valve switchings controlled purely by an open-loop system, i.e., without an internal coupling. Such switchings have the advantage that they are operable at lower pressure levels, whereby better hydraulic efficiencies are achieved.
Presently, effects resulting from the electromagnetic hysteresis in the area of electro-hydraulic pilot stages and from the static friction of the subsequent slide of the cooling valve are largely eliminated by a relatively low rate of a chopper frequency of 1 kHz of the current control as well as an actively superimposed dither having a frequency of approximately 125 Hz, which the actuated subsequent slide cannot dynamically follow, however. The underlying basic idea in this case is that of triggering micro-movements in the area of the pilot stage which therefore no longer switches into the static friction condition, while the electromagnetic hysteresis is simultaneously reduced.
If an accuracy or a reproducibility of the actuation of a cooling valve or, in general, of a valve cannot be ensured to the desired extent, a wide range of problems may occur during operation. The problems range from reduced comfort, as perceived by the driver, and so-called gear blockers, to burnt clutches or damage to bearings and gearwheels, all of which are caused by insufficient cooling and result in transmission failures and complaints.
The problem addressed by the present invention is therefore that of providing a method for actuating a valve device as a function of a characteristic curve, in order to be able to operate a valve device with a desirably high level of accuracy.